Recently, a high-speed cellular wireless communication scheme such as LTE (Long Term Evolution) and WiMAX has been used practically, which has significantly improved a communication rate of wireless communication service received by mobile users. Moreover, when a fourth-generation cellular wireless communication scheme such as LTE-A (LTE-Advanced) is introduced, it is expected that the communication rate further improves.
In addition, the number of mobile users is increasing rapidly, and an application requiring a high data rate is being used more widely. As a result, the progress of the cellular wireless communication scheme has not satisfied all needs of mobile users. Thus, the introduction of small cells is promoted in order to complement macro cells and increase communication capacity. The small cell is a concept including a femtocell, a nanocell, a picocell, and a micro cell, for example. The small cell is typically introduced by arranging a base station (also referred to as an access point) smaller than a base station of a macro cell (eNB (evolved Node B) in LTE, for example). However, in an area where a macro cell and a small cell overlap, there occurs a risk that radio signals transmitted and received by the small cell will cause interference to terminals connected to the macro cell.
In order to avoid the risk of interference with introduction of a small cell, the following Patent Literature 1 proposes a method of cooperatively controlling transmission power and transmission rates of a macro cell and a small cell. The following Patent Literature 2 proposes a method of cooperatively controlling transmission beams of a macro and a small cell.